1. Field of the Invention
The present invention relates to a system monitoring unit suitable for, for example, system debugging.
2. Description of the Related Art
Conventionally, for debugging a program in a target system, an in-circuit emulator has been used that emulates the operation of a central processing unit (CPU) of the target system.
In debugging using the in-circuit emulator, there are two known techniques. In one (see Japanese Unexamined Patent Application Publication Nos. 11-108998 and 7-21054), after stopping the operation of an internal CPU, a serial transmission line is used to transmit a predetermined command from a debugging unit. In another (see Japanese Unexamined Patent Application Publication No. 11-232134), by using a testing chip corresponding to an internal CPU, predetermined commands are transmitted from a debugging unit to all signal lines in the chip.
In the first technique, a debugging circuit must be separately provided, and internal information obtained during the operation of the internal CPU cannot be output because debugging must be performed when the internal CPU has been ordered to stop.
In the second technique, developing the testing chip requires time and money, and it is difficult to develop a testing chip which is suitable for use with high-speed execution speed of internal CPUs.